Corticosterone analgesia is mediated by the spinal production of neuroactive metabolites that enhance GABAergic inhibitory transmission on dorsal horn rat neurons

Prophylactic dexamethasone for rebound pain after peripheral nerve block in adult surgical patients: systematic review, meta-analysis, and trial sequential analysis of randomised controlled trials

BACKGROUND

Rebound pain occurs after the resolution of peripheral nerve block and hampers patient recovery in the postoperative period. We sought to synthesise available data from randomised controlled trials (RCTs) evaluating the efficacy of prophylactic dexamethasone for rebound pain in adult patients undergoing surgery with a peripheral nerve block.

METHODS

In this systematic review and meta-analysis, RCTs reporting rebound pain and use of dexamethasone in the context of a peripheral nerve block were searched in various databases and updated in May 2023. The primary outcome was the incidence of rebound pain; secondary outcomes included the severity and time to onset of rebound pain, patient satisfaction with pain control, sleep disturbance because of pain, and adverse effects of dexamethasone. Subgroup analysis was conducted based on the effect of route of administration (intravenous or perineural) on the incidence of rebound pain. Trial sequential analysis was performed to rule out the possibility of a false positive result.

RESULTS

Seven RCTs comprising 574 patients were included in this review. The dexamethasone group was associated with a reduction in the incidence of rebound pain with an odds ratio of 0.16 (95% confidence interval 0.10-0.27, P=0.00, I2=0%) compared with the control group. Trial sequential analysis confirmed the adequate information size for the beneficial effect of dexamethasone. Subgroup analysis showed that both intravenous and perineural administration were associated with a significant reduction in the incidence of rebound pain.

CONCLUSIONS

Current evidence suggests that both intravenous and perineural dexamethasone reduce the incidence of rebound pain after a peripheral nerve block provided for postoperative analgesia.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42023424031.

Corticosteroids as Selective and Effective Modulators of Glycine Receptors

The mechanism of the negative impact of corticosteroids on the induction and progress of mental illness remains unclear. In this work, we studied the effects of corticosteroids on the activity of neuronal glycine receptors (GlyR) and GABA-A receptors (GABAAR) by measuring the chloride current induced by the application of GABA (2 or 5 μM) to isolated cerebellar Purkinje cells (IGABA) and by the application of glycine (100 μM) to pyramidal neurons of the rat hippocampus (IGly). It was found that corticosterone, 5α-dihydrodeoxycorticosterone, allotetrahydrocorticosterone, cortisol, and 17α,21-dihydroxypregnenolone were able to accelerate the desensitization of the IGly at physiological concentrations (IC50 values varying from 0.39 to 0.72 μM). Next, cortisone, 11-deoxycortisol, 11-deoxycorticosterone, 5β-dihydrodeoxycorticosterone, and tetrahydrocorticosterone accelerated the desensitization of IGly with IC50 values varying from 10.3 to 15.2 μM. Allotetrahydrocorticosterone and tetrahydrocorticosterone potentiated the IGABA albeit with high EC50 values (18-23 μM). The rest of the steroids had no effect on IGABA in the range of concentrations of 1-100 μM. Finally, our study has suggested a structural relationship of the 3β-hydroxyl group/3-oxo group with the selective modulatory activity on GlyRs in contrast to the 3α-hydroxyl group that is pivotal for GABAARs. In summary, our results suggest that increased GlyR desensitization by corticosteroids may contribute to brain dysfunction under chronic stress and identify corticosteroids for further development as selective modulators of GlyRs.

Effects of Corticosterone on the Excitability of Glutamatergic and GABAergic Neurons of the Adolescent Mouse Superficial Dorsal Horn

Stress evokes age-dependent effects on pain sensitivity and commonly occurs during adolescence. However, the mechanisms linking adolescent stress and pain remain poorly understood, in part due to a lack of information regarding how stress hormones modulate the function of nociceptive circuits in the adolescent CNS. Here we investigate the short- and long-term effects of corticosterone (CORT) on the excitability of GABAergic and presumed glutamatergic neurons of the spinal superficial dorsal horn (SDH) in Gad1-GFP mice at postnatal days (P)21-P34. In situ hybridization revealed that glutamatergic SDH neurons expressed significantly higher mRNA levels of both glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) compared to adjacent GABAergic neurons. The incubation of spinal cord slices with CORT (90 min) evoked select long-term changes in spontaneous synaptic transmission across both cell types in a sex-dependent manner, without altering the intrinsic firing of either Gad1-GFP+ or GFP- neurons. Meanwhile, the acute bath application of CORT significantly decreased the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs), as well as the frequency of miniature inhibitory postsynaptic currents (mIPSCs), in both cell types leading to a net reduction in the balance of spontaneous excitation vs. inhibition (E:I ratio). This CORT-induced reduction in the E:I ratio was not prevented by selective antagonists of either GR (mifepristone) or MR (eplerenone), although eplerenone blocked the effect on mEPSC amplitude. Collectively, these data suggest that corticosterone modulates synaptic function within the adolescent SDH which could influence the overall excitability and output of the spinal nociceptive network.

Grape Polyphenols May Prevent High-Fat Diet-Induced Dampening of the Hypothalamic-Pituitary-Adrenal Axis in Male Mice

Context 

Chronic high-fat diet (HFD) consumption causes obesity associated with retention of bile acids (BAs) that suppress important regulatory axes, such as the hypothalamic-pituitary-adrenal axis (HPAA). HFD impairs nutrient sensing and energy balance due to a dampening of the HPAA and reduced production and peripheral metabolism of corticosterone (CORT).

Objective

We assessed whether proanthocyanidin-rich grape polyphenol (GP) extract can prevent HFD-induced energy imbalance and HPAA dysregulation.

Methods

Male C57BL6/J mice were fed HFD or HFD supplemented with 0.5% w/w GPs (HFD-GP) for 17 weeks.

Results

GP supplementation reduced body weight gain and liver fat while increasing circadian rhythms of energy expenditure and HPAA-regulating hormones, CORT, leptin, and PYY. GP-induced improvements were accompanied by reduced mRNA levels of Il6, Il1b, and Tnfa in ileal or hepatic tissues and lower cecal abundance of Firmicutes, including known BA metabolizers. GP-supplemented mice had lower concentrations of circulating BAs, including hydrophobic and HPAA-inhibiting BAs, but higher cecal levels of taurine-conjugated BAs antagonistic to farnesoid X receptor (FXR). Compared with HFD-fed mice, GP-supplemented mice had increased mRNA levels of hepatic Cyp7a1 and Cyp27a1, suggesting reduced FXR activation and more BA synthesis. GP-supplemented mice also had reduced hepatic Abcc3 and ileal Ibabp and Ostβ, indicative of less BA transfer into enterocytes and circulation. Relative to HFD-fed mice, CORT and BA metabolizing enzymes (Akr1d1 and Srd5a1) were increased, and Hsd11b1 was decreased in GP supplemented mice.

Conclusion

GPs may attenuate HFD-induced weight gain by improving hormonal control of the HPAA and inducing a BA profile with less cytotoxicity and HPAA inhibition, but greater FXR antagonism.

Role of GABAergic system in the comorbidity of pain and depression

Patients with chronic pain often suffer with depressive symptoms, and these two conditions can be aggravated by each other over time, leading to an increase in symptom intensity and duration. The comorbidity of pain and depression poses a significant challenge to human health and quality of life, as it is often difficult to diagnose early and treat effectively. Therefore, exploring the molecular mechanisms underlying the comorbidity of chronic pain and depression is crucial to identifying new therapeutic targets for treatment. However, understanding the pathogenesis of comorbidity requires examining interactions among multiple factors, which calls for an integrative perspective. While several studies have explored the role of the GABAergic system in pain and depression, fewer have examined its interactions with other systems involved in their comorbidity. Here, we review the evidence that the role of GABAergic system in the comorbidity of chronic pain and depression, as well as the interactions between the GABAergic system and other secondary systems involved in pain and depression comorbidity, providing a comprehensive understanding of their intricate interplay.

Effect of Adding Perineural Methylprednisolone to Peripheral Nerve Blocks Combined With Intravenous Dexamethasone for Prolonged Postdischarge Analgesia After Fast-track Total Knee Arthroplasty: A Randomized Controlled Trial

OBJECTIVES

Patients undergoing total knee arthroplasty (TKA) may experience moderate-to-severe subacute pain after hospital discharge that may be undermanaged. We aimed to evaluate the effect of methylprednisolone added to ultrasound-guided peripheral nerve blocks (PNBs) combined with multimodal analgesia including intravenous dexamethasone for prolonged analgesia after early discharge.

MATERIALS AND METHODS

We randomized 80 patients who underwent fast-track TKA into 2 groups. All patients received a periarticular injection, PNBs, and multiple doses of intravenous dexamethasone. The methylprednisolone group received 140 mg methylprednisolone in PNBs, while the nonmethylprednisolone group did not. The primary outcome was the incidence of moderate-to-severe pain (Numerical Rating Scale ≥4) during the first 12 postdischarge days. The secondary outcomes included pain scores until 3 postoperative months, incidence of rebound pain, functional performances, patient satisfaction, and adverse events.

RESULTS

No significant between-group differences were noted in the incidence of moderate-to-severe pain during the first 12 postdischarge days (nonmethylprednisolone vs. methylprednisolone groups: 70% vs. 69.2%, P=0.941). However, this incidence was significantly higher in the methylprednisolone group between 2 weeks and 1 month (P=0.015) and between 1 and 3 months (P=0.004) postoperatively. No between-group differences in the Numerical Rating Scale scores at the postdischarge time points, incidence of rebound pain, and functional performance results were noted.

DISCUSSION

Adding perineural methylprednisolone to ultrasound-guided PNBs for multimodal analgesia with intravenous dexamethasone did not prolong analgesia and improved the functional ability after fast-track TKA within 12 postdischarge days. However, the incidence moderate-to-severe pain may increase between the 2-week and 3-month follow-up.

Early exposure to environmental enrichment protects male rats against neuropathic pain development after nerve injury

Because environmental elements modify chronic pain development and endogenous mechanisms of pain control are still a great therapeutic source, we investigated the effects of an early exposure to environmental enrichment (EE) in a translational model of neuropathic pain. Young male rats born and bred in an enriched environment, which did not count on running wheel, underwent chronic constriction injury (CCI) of sciatic nerve. EE abolished neuropathic pain behavior 14 days after CCI. Opioid receptors' antagonism reversed EE-analgesic effect. β-endorphin and met-enkephalin serum levels were increased only in EE-CCI group. Blockade of glucocorticoid receptors did not alter EE-analgesic effect, although corticosterone circulating levels were increased in EE animals. In the spinal cord, EE controlled CCI-induced serotonin increase. In DRG, EE blunted the expression of ATF-3 after CCI. Surprisingly, EE-CCI group showed a remarkable preservation of sciatic nerve fibers compared to NE-CCI group. This work demonstrated global effects induced by an EE protocol that explain, in part, the protective role of EE upon chronic noxious stimulation, reinforcing the importance of endogenous mechanisms in the prevention of chronic pain development.

Excitability of Rat Superficial Dorsal Horn Neurons Following a Neonatal Immune Challenge

Previous studies have shown that neonatal exposure to a mild inflammatory challenge, such as lipopolysaccharide (LPS, Salmonella enteriditis) results in altered pain behaviors later in life. To further characterize the impact of a neonatal immune challenge on pain processing, we examined the excitability of superficial dorsal horn (SDH) neurons following neonatal LPS exposure and subsequent responses to noxious stimulation at three time-points during early postnatal development. Wistar rats were injected with LPS (0.05 mg/kg i.p.) or saline on postnatal days (PNDs) 3 and 5, and later subjected to the formalin test at PNDs 7, 13, and 22. One hour after formalin injection into the plantar hindpaw, animals were euthanized (Ketamine, 100 mg/kg i.p.) and transverse slices from the lumbosacral spinal cord were prepared. Whole-cell patch-clamp recordings were made from SDH neurons (KCH₃SO₄-based internal, 22–24°C) on the ipsi- and contralateral sides of the spinal cord. Depolarising current steps were injected into SDH neurons to categorize action potential (AP) discharge. In both saline- and LPS-treated rats we observed age-related increases the percentage of neurons exhibiting tonic-firing, with concurrent decreases in single-spiking, between PND 7 and 22. In contrast, neonatal exposure to LPS failed to alter the proportions of AP discharge patterns at any age examined. We also assessed the subthreshold currents that determine AP discharge in SDH neurons. The rapid outward potassium current, I_Ar decreased in prevalence with age, but was susceptible to neonatal LPS exposure. Peak I_Ar current amplitude was greater in ipsilateral vs. contralateral SDH neurons from LPS-treated rats. Spontaneous excitatory synaptic currents (sEPSCs) were recorded to assess network excitability. Age-related increases were observed in sEPSC frequency and time course, but not peak amplitude, in both saline- and LPS-treated rats. Furthermore, sEPSC frequency was higher in ipsilateral vs. contralateral SDH neurons in LPS-treated animals. Taken together, these data suggest a neonatal immune challenge does not markedly affect the intrinsic properties of SDH neurons, however, it can increase the excitability of local spinal cord networks via altering the properties of rapid A-type currents and excitatory synaptic connections. These changes, made in neurons within spinal cord pain circuits, have the capacity to alter nociceptive signaling in the ascending pain pathway.

Lumbar Epidural Corticosteroid Injection Reduces Subacute Pain and Improves Knee Function in the First Six Weeks After Total Knee Arthroplasty: A Double-Blinded Randomized Trial

BACKGROUND

Pain control immediately following total knee arthroplasty (TKA) has been a focus for orthopaedists. However, control of subacute pain, which may persist up to 3 months, is usually not optimized. The efficacy of epidural corticosteroids in reducing pain after surgery is documented, but data on their efficacy in controlling subacute pain after TKA are lacking. Our aim was to investigate the efficacy of an epidural corticosteroid in controlling pain in the first 3 months following TKA using a double-blinded randomized clinical trial.

METHODS

One hundred and eight patients with osteoarthritis of the knee who underwent TKA and received analgesic drugs through an epidural catheter for 48 hours were randomized to receive either 40 mg (1 mL) of triamcinolone acetonide plus 5 mL of 1% lidocaine, or 6 mL of 1% lidocaine alone before catheter removal. The outcomes of interest were pain level during motion and at rest, knee function, and range of motion, which were recorded up to 3 months after surgery. Multilevel regression models were used to estimate the differences between groups.

RESULTS

The corticosteroid + lidocaine group had a lower average level of pain during motion compared with the lidocaine-only group, as measured by a visual analog scale (VAS), from day 3 to 7 weeks postoperatively (p < 0.05). At 7 weeks, the mean difference was -7 points (95% confidence interval [CI], -12.8 to -1.0 points; p = 0.033). The corticosteroid + lidocaine group also had a better mean overall modified Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score at 6 weeks postoperatively (28 compared with 33 points; 95% CI, -8.6 to -0.6 points; p = 0.03). There was no difference between the groups in the level of pain at rest and knee range of motion during the 3-month period (p > 0.05).

CONCLUSIONS

Lumbar epidural corticosteroid injection reduced pain during motion for 7 weeks and provided better knee function at 6 weeks postoperatively compared with lidocaine alone. There was no difference detected with respect to pain at rest and knee range of motion during the 3-month follow-up. Epidural corticosteroids could improve patient satisfaction during the early weeks of recovery after TKA.

LEVEL OF EVIDENCE

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Maternal separation stress leads to resilience against neuropathic pain in adulthood

Early life stress (ELS) leads to a permanent reprogramming of biochemical stress response cascades that may also be relevant for the processing of chronic pain states such as neuropathy. Despite clinical evidence, little is known about ELS-related vulnerability for neuropathic pain and the possibly underlying etiology.

In the framework of experimental studies aimed at investigating the respective relationships we used the established ELS model of maternal separation (MS). Rat dams and neonates were separated for 3 h/day from post-natal day 2–12. At adulthood, noxious mechanical and thermal thresholds were assessed before and during induction of neuropathic pain by chronic constriction injury (CCI). The potential involvement of spinal glutamatergic transmission, glial cells, pro-inflammatory cytokines and growth factors was studied by using qPCR.

MS per se did not modify pain thresholds. But, when exposed to neuropathic pain, MS rats exhibited a marked reduction of thermal sensitivity and a delayed development of mechanical allodynia/hyperalgesia when compared to control animals. Also, MS did not alter glucocorticoid receptor mRNA levels, but prevented the CCI-induced down-regulation of NR1 and NR2 sub-units of the NMDA receptor and of the glutamate transporter EAAT3 as observed at 21 days post-surgery. Additionally, CCI-provoked up-regulation of glial cell markers was either prevented (GFAP for astrocytes) or dampened (Iba1 for microglia) by MS. Pro-inflammatory cytokine mRNA expression was either not affected (IL-6) or reduced (IL-1β) by MS shortly after CCI. The growth factors GDNF and NGF were only slightly downregulated 4 days after CCI in the MS-treated animals. The changes in glutamatergic signaling, astroglial and cytokine activation as well as neurotrophin expression could, to some extent, explain these changes in pain behavior. Taken together, the results obtained in the described experimental conditions support the mismatch theory of chronic stress where an early life stress, rather than predisposing individuals to certain pathologies, renders them resilient.

Chronic Social Stress Time-Dependently Affects Neuropathic Pain-Related Cold Allodynia and Leads to Altered Expression of Spinal Biochemical Mediators

Clinical data have shown that chronic exposure to stress may be accompanied by an enhancement of inflammation-related pain sensitivity. In this context, little is however known on the impact of stress on neuropathic pain. In the present study we addressed this issue by combining the chronic constriction injury (CCI) model with an ongoing social stress (OSS) paradigm. Cold plate and von Frey tests were performed in 48 rats divided into four groups: OSS exposed to OSS, CCI subjected to chronic nerve constriction, OSS+CCI with a combination of neuropathy and stress and CON, a control group lacking any manipulation. While we did not observe any stress-related differences in mechanical sensitivity throughout the observation period, CCI rats were more sensitive to cold stimulation than OSS+CCI in the initial phase of neuropathy. A switch was observed at a later stage, leading to a hypersensitivity of the OSS+CCI compared to the CCI rats. At this time point we investigated the spinal mRNA expression of neuron and glia related molecules potentially involved in neuropathic pain and stress. The combination of psychosocial stress and neuropathic pain seemed to enhance glial cell activation, pro-inflammatory cytokine and neurotrophic factor mRNA levels, rather than glutamatergic transmission. Our data show that long lasting social stress may lead to time-dependent alteration of neuropathy-related cold pain sensitivity while mechanically-induced pain remains unchanged.

Lifetime Modulation of the Pain System via Neuroimmune and Neuroendocrine Interactions

Chronic pain is a debilitating condition that still is challenging both clinicians and researchers. Despite intense research, it is still not clear why some individuals develop chronic pain while others do not or how to heal this disease. In this review, we argue for a multisystem approach to understand chronic pain. Pain is not only to be viewed simply as a result of aberrant neuronal activity but also as a result of adverse early-life experiences that impact an individual's endocrine, immune, and nervous systems and changes which in turn program the pain system. First, we give an overview of the ontogeny of the central nervous system, endocrine, and immune systems and their windows of vulnerability. Thereafter, we summarize human and animal findings from our laboratories and others that point to an important role of the endocrine and immune systems in modulating pain sensitivity. Taking "early-life history" into account, together with the past and current immunological and endocrine status of chronic pain patients, is a necessary step to understand chronic pain pathophysiology and assist clinicians in tailoring the best therapeutic approach.

Neuroactive steroids, nociception and neuropathic pain: A flashback to go forward

The present review discusses the potential role of neurosteroids/neuroactive steroids in the regulation of nociceptive and neuropathic pain, and recapitulates the current knowledge on the main mechanisms involved in the reduction of pain, especially those occurring at the dorsal horn of the spinal cord, a crucial site for nociceptive processing. We will make special focus on progesterone and its derivative allopregnanolone, which have been shown to exert remarkable actions in order to prevent or reverse the maladaptive changes and pain behaviors that arise after nervous system damage in various experimental neuropathic conditions.

Favouring inhibitory synaptic drive mediated by GABA(A) receptors in the basolateral nucleus of the amygdala efficiently reduces pain symptoms in neuropathic mice

Pain is an emotion and neuropathic pain symptoms are modulated by supraspinal structures such as the amygdala. The central nucleus of the amygdala is often called the 'nociceptive amygdala', but little is known about the role of the basolateral amygdala. Here, we monitored the mechanical nociceptive thresholds in a mouse model of neuropathic pain and infused modulators of the glutamate/GABAergic transmission in the basolateral nucleus of the amygdala (BLA) via chronically-implanted cannulas. We found that an N-methyl-D-aspartate-type glutamate receptor antagonist (MK-801) exerted a potent antiallodynic effect, whereas a transient allodynia was induced after perfusion of bicuculline, a GABA(A) receptor antagonist. Potentiating GABA(A) receptor function using diazepam or etifoxine (a non-benzodiazepine anxiolytic) fully but transiently alleviated mechanical allodynia. Interestingly, the antiallodynic effect of etifoxine disappeared in animals that were incapable of producing 3α-steroids. Diazepam had a similar effect but of shorter duration. As indicated by patch-clamp recordings of BLA neurons, these effects were mediated by a potentiation of GABA(A) receptor-mediated synaptic transmission. Together with a presynaptic elevation of miniature inhibitory postsynaptic current frequency, the duration and amplitude of GABA(A) miniature inhibitory postsynaptic currents were also increased (postsynaptic effect). The analgesic contribution of endogenous neurosteroid seemed to be exclusively postsynaptic. This study highlights the importance of the BLA and the local inhibitory/excitatory neuronal network activity while setting the mechanical nociceptive threshold. Furthermore, it appears that promoting inhibition in this specific nucleus could fully alleviate pain symptoms. Therefore, the BLA could be a novel interesting target for the development of pharmacological or non-pharmacological therapies.